The present invention relates generally to a system and method for joining two components to one another, particularly where one of the two components is a hardened metal, and more specifically to a system and method for attaching a stud or other appurtenance to a specific location on a length of steel rail for the purpose of attaching a signal wire to the stud.
Railroad signaling systems are essential for enabling safe and efficient movement of rail traffic. Many modern railroad signal systems employ a track circuit to detect the presence of a train within a section of track known as a signal block. The basic principle behind the track circuit involves the connection of the two rails by the wheels and axle of locomotives to short out an electrical circuit. This circuit is monitored by electrical equipment to detect the absence of the trains. An integral part of the track circuit is the two parallel running rails on which a train runs. Various types of signal devices are typically connected to these rails to complete the track circuit. Known techniques for connecting a wire to a rail include exothermic welding processes where the wire is welded to the rail. Other techniques include compressing a metal sleeve including the wire in a hole drilled in the rail or clamping a wire directly to the rail. Many signaling system incidents are known to be caused by failures at the rail-wire interface, where track wires, bond wires, or propulsion-current bond wires are attached to the rails to provide an electrical path for controlling train control signals. These failures contribute to train delays and additional maintenance costs for emergency and unplanned repairs and are highly undesirable for these and other reasons.
As indicated above, signal wires are attached to rails to allow for positive train control and to sense breaks in the rails for avoiding accidents. A reliable signal wire-to-rail connection is essential for signal system functionality and failures cause service disruptions and can affect the integrity of the rail, leading to rail failure. Currently used methods for attaching a signal wire to a length of track involve the use of an appurtenance or stud that is attached directly to the rail. The signal wire is then attached or connected to the stud. Common attachment methodologies include brazing, soldering, drilling, and/or clamping the stud/wire to the rail. Many brazing methods require preheating the rail section to which the stud will be attached and then precisely controlling the rate of cooling to avoid the undesirable formation of untempered martensite in the rail. With brazing methodologies there is also the risk of liquid metal embrittlement as the rail is under tensile stress to maintain neutral temperature and a liquid metal is present during the process. Accordingly, it is a common precautionary practice to locate the studs at the neutral axis of the rail due to the possible formation of a brittle layer around the joint caused by overheating of the stud/wire to rail connection point. The placement of welds/braze joints on the head of the rail is known to have resulted in the formation of martensite in the head of the rail, which initiated cracks that led to several train derailments; thus the neutral axis is generally safer from a catastrophic failure perspective. However, placement at this location makes the wire harnesses susceptible to snagging by maintenance equipment and the formation of martensite in this area may still lead to cracking and rail failure. Furthermore, most known attachment methodologies require a degree of operator skill, the absence of which may result in inconsistent or incorrect installations and ultimately in failure of the stud/wire connection, particularly in mass production. Thus, there is an ongoing need for an improved system and method for attaching a stud or appurtenance to a specific location on a length of steel rail.